Quote Originally Posted by Mr.Fixit-Norm View Post
That’s interesting evert, I wonder if there’s an optimum seal resistance ? If when I’ve got it apart I could push the piston back to its ‘at rest’ position, remove the spring, find a steel tube that fits over the piston rod then fit a plate to the top on which I could place weights. Weighing the tube and plate I can then mount the cylinder vertically in a clamp and start adding weights til the piston moves.

Might be an interesting experiment
That experiment will give some useful insight. It would be interesting to se how power changes with different seal resistance.
I'd guess that there's different "best" seal resistance for different types of seals and guns. Some seals have thin sealing lips that expand when pessurized, this probably causes a lot of friction that you cant detect with the sliding test.
I prefer to try different seals from different makers before sizing.
You can often find one that fits and does what you want without removing any material if you have several to choose from.
But that big box of seals costs a bit of money.....